The present invention relates generally to tire retreading, and more particularly, the present invention relates to securing an annular elastomeric sealing ring to an inner peripheral tire bead such that an endless, ring-shaped air tight seal is created along the entire tire bead circumference.
Examples of processes which utilize a single outer curing envelope and a pair of sealing rings for retreading a tire are discussed in the present assignee""s U.S. Pat. No. 5,518,384 issued to Presti et al. and U.S. Pat. No. 5,098,268 issued to Robinson. Worn tread on a used tire casing is buffed off to a profile suitable for mounting a new tread. Then, a pre-cured and buffed tread is adhered about the periphery of the casing with a laminate of uncured cushion gum cemented between the tread and the casing. An outer annular elastomeric curing envelope having an inwardly-opening U-shaped radial cross section is positioned over the new tread and a portion of the outer sidewalk of the tire casing. A pair of annular elastomeric sealing rings are secured about the inner peripheral beads of the tire casing and cooperate with the outer curing envelope to encase the tire casing outer sidewalk. A vacuum is drawn through a valve in the outer curing envelope for stretching the envelope into intimate contact with all surfaces of the tread. The tire is then placed in an autoclave for several hours at an elevated temperature and pressure to cure the gum and positively bond the casing and tread. The outer curing envelope and sealing rings are removed and the retreaded tire is ready for use.
An important step in the above-described tire retreading process is the step of securing the sealing ring to the tire beads. The sealing rings must engage and form an airtight seal with the tire beads so that a vacuum is properly drawn. The vacuum ensures that air or steam does not penetrate into the cushion gum during curing of the gum because the presence of air bubbles, or pockets of air, between the curing envelope and the tire will prevent proper curing of the gum and will cause tread distortion. In addition, air pockets prevent pressure from being uniformly applied over the entire bonding area which also causes tread distortion.
U.S. Pat. No. 5,098,268 discloses a two step process of first mounting the sealing rings on the tire casing, and then separately mounting the rims within the inner periphery of the sealing rings to compress the sealing rings to the tire beads. See FIG. 2 and column 4, lines 26-31, of the ""268 patent. In FIG. 4 and column 4, lines 40-45, of the ""268 patent, an alternate embodiment is disclosed which utilizes a bonding agent to bond the sealing rings onto the rims to form a unitary structure capable of being quickly mounted. An advantage of the rim disclosed in the ""268 patent is that it exerts substantially uniform pressure on the sealing ring and tire bead throughout the entire circumferences of the sealing ring and tire bead. Thus, the uniform pressure results in the formation of a proper air tight 360xc2x0 ring, or band, of seal.
U.S. Pat. No. 5,518,384 discloses the use of an expandable and retractable rim to compress a sealing ring into airtight engagement with a tire bead. The rim includes a ratchet mechanism which enables the diameter of the rim to be incrementally increased or decreased. The advantage of the adjustable rim of the ""384 patent is that it can be utilized on a variety of tires having various bead circumferences.
Although the above-referenced sealing ring and rim assemblies are satisfactory for their intended purposes, there is a need for an improved sealing ring and rim assembly which is easy to mount and dismount on various tire types and sizes. The sealing ring and rim assembly should be adjustable so that it can be used on various tire bead sizes within a range of sizes. The assembly should also be capable of exerting substantially uniform pressure along the entire circumference of the tire bead so that a proper air tight seal is created. In addition, the sealing ring and rim assembly should be easy to use and inexpensive to manufacture.
With the foregoing in mind, a primary object of the present invention is to provide a novel sealing ring and rim assembly for use with an outer curing envelope to retread tire casings of various sizes, configurations and bead circumferences.
Another object of the present invention is to provide an improved sealing ring and rim assembly which can be readily mounted onto a tire such that outward radial pressure is uniformly applied along the entire circumference of the tire bead to create an effective air tight seal between the tire bead and the sealing ring.
A further object of the present invention is to provide an adjustable sealing ring and rim assembly which is capable of re-use over an extended period.
A still further object of the present invention is to provide a sealing ring and rim assembly which is easy to use and inexpensive to manufacture.
More specifically, the present invention provides a sealing ring and rim assembly for use in retreading a tire casing having opposed sidewalls terminating in a pair of inner peripheral beads. The assembly includes a rigid annular rim having a fixed predetermined diameter and capable of being readily positioned within one of the inner peripheral beads of the tire casing. An annular elastomeric sealing ring is seated on the annular rim and is capable of being expanded relative to the rim into airtight engagement with the peripheral bead of the tire casing. The sealing ring is expandable by an annular inflatable bladder located on the rim and positioned between the rim and the sealing ring. When the bladder is inflated, the sealing ring is forced to expand radially outward relative to the rim, and when the bladder is deflated, the sealing ring is permitted to contract radially inward relative to the rim.